Ways to convert an InputStream to a String

Reference:

[1] https://stackoverflow.com/questions/309424/read-convert-an-inputstream-to-a-string

Ways to convert an InputStream to a String:

1. Using IOUtils.toString (Apache Utils)

   String result = IOUtils.toString(inputStream, StandardCharsets.UTF_8);

2. Using CharStreams (guava)

   String result = CharStreams.toString(new InputStreamReader(
         inputStream, Charsets.UTF_8));

3. Using Scanner (JDK)

   Scanner s = new Scanner(inputStream).useDelimiter("\\A");
   String result = s.hasNext() ? s.next() : "";

4. Using Stream Api (Java 8). Warning: This solution convert different line breaks (like \r\n) to \n.

   String result = new BufferedReader(new InputStreamReader(inputStream))
     .lines().collect(Collectors.joining("\n"));

5. Using parallel Stream Api (Java 8). Warning: This solution convert different line breaks (like \r\n) to \n.

   String result = new BufferedReader(new InputStreamReader(inputStream)).lines()
      .parallel().collect(Collectors.joining("\n"));

6. Using InputStreamReader and StringBuilder (JDK)

   final int bufferSize = 1024;
   final char[] buffer = new char[bufferSize];
   final StringBuilder out = new StringBuilder();
   Reader in = new InputStreamReader(inputStream, "UTF-8");
   for (; ; ) {
       int rsz = in.read(buffer, 0, buffer.length);
       if (rsz < 0)
           break;
       out.append(buffer, 0, rsz);
   }
   return out.toString();

7. Using StringWriter and IOUtils.copy (Apache Commons)

   StringWriter writer = new StringWriter();
   IOUtils.copy(inputStream, writer, "UTF-8");
   return writer.toString();

8. Using ByteArrayOutputStream and inputStream.read (JDK)

   ByteArrayOutputStream result = new ByteArrayOutputStream();
   byte[] buffer = new byte[1024];
   int length;
   while ((length = inputStream.read(buffer)) != -1) {
       result.write(buffer, 0, length);
   }
   // StandardCharsets.UTF_8.name() > JDK 7
   return result.toString("UTF-8");

9. Using BufferedReader (JDK). Warning: This solution convert different line breaks (like \n\r) to line.separator system property (for example, in Windows to "\r\n").

   String newLine = System.getProperty("line.separator");
   BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
   StringBuilder result = new StringBuilder();
   String line; boolean flag = false;
   while ((line = reader.readLine()) != null) {
       result.append(flag? newLine: "").append(line);
       flag = true;
   }
   return result.toString();

10. Using BufferedInputStream and ByteArrayOutputStream (JDK)

    BufferedInputStream bis = new BufferedInputStream(inputStream);
    ByteArrayOutputStream buf = new ByteArrayOutputStream();
    int result = bis.read();
    while(result != -1) {
        buf.write((byte) result);
        result = bis.read();
    }
    // StandardCharsets.UTF_8.name() > JDK 7
    return buf.toString("UTF-8");

11. Using inputStream.read() and StringBuilder (JDK). Warning: This solution has problem with Unicode, for example with Russian text (work correctly only with non-Unicode text)

    int ch;
    StringBuilder sb = new StringBuilder();
    while((ch = inputStream.read()) != -1)
        sb.append((char)ch);
    reset();
    return sb.toString();

Warning:

1. Solutions 4, 5 and 9 convert different line breaks to one.

2. Solution 11 can't work correctly with Unicode text

Performance tests

Performance tests for small String (length = 175), url in github (mode = Average Time, system = Linux, score 1,343 is the best):

              Benchmark                        Mode  Cnt   Score   Error  Units
8. ByteArrayOutputStream and read (JDK)        avgt   10   1,343 ± 0,028  us/op
6. InputStreamReader and StringBuilder (JDK)   avgt   10   6,980 ± 0,404  us/op
10.BufferedInputStream, ByteArrayOutputStream  avgt   10   7,437 ± 0,735  us/op
11.InputStream.read() and StringBuilder (JDK)  avgt   10   8,977 ± 0,328  us/op
7. StringWriter and IOUtils.copy (Apache)      avgt   10  10,613 ± 0,599  us/op
1. IOUtils.toString (Apache Utils)             avgt   10  10,605 ± 0,527  us/op
3. Scanner (JDK)                               avgt   10  12,083 ± 0,293  us/op
2. CharStreams (guava)                         avgt   10  12,999 ± 0,514  us/op
4. Stream Api (Java 8)                         avgt   10  15,811 ± 0,605  us/op
9. BufferedReader (JDK)                        avgt   10  16,038 ± 0,711  us/op
5. parallel Stream Api (Java 8)                avgt   10  21,544 ± 0,583  us/op

Performance tests for big String (length = 50100), url in github (mode = Average Time, system = Linux, score 200,715 is the best):

              Benchmark                        Mode  Cnt   Score        Error  Units
8. ByteArrayOutputStream and read (JDK)        avgt   10   200,715 ±   18,103  us/op
1. IOUtils.toString (Apache Utils)             avgt   10   300,019 ±    8,751  us/op
6. InputStreamReader and StringBuilder (JDK)   avgt   10   347,616 ±  130,348  us/op
7. StringWriter and IOUtils.copy (Apache)      avgt   10   352,791 ±  105,337  us/op
2. CharStreams (guava)                         avgt   10   420,137 ±   59,877  us/op
9. BufferedReader (JDK)                        avgt   10   632,028 ±   17,002  us/op
5. parallel Stream Api (Java 8)                avgt   10   662,999 ±   46,199  us/op
4. Stream Api (Java 8)                         avgt   10   701,269 ±   82,296  us/op
10.BufferedInputStream, ByteArrayOutputStream  avgt   10   740,837 ±    5,613  us/op
3. Scanner (JDK)                               avgt   10   751,417 ±   62,026  us/op
11.InputStream.read() and StringBuilder (JDK)  avgt   10  2919,350 ± 1101,942  us/op